1. Field of the Invention
The present invention relates to an electrically-powered steering apparatus for assisting steering of wheels by detecting steering condition and generating an assist force corresponding to the steering condition by means of a motor.
2. Description of Related Art
A conventional electrically-powered steering apparatus detects a steering torque generated in a steering shaft by means of a torque sensor and determines a current instruction value to be outputted to a driving circuit for driving a motor based on this detected steering torque, a vehicle velocity detected by other sensor and the like. After that, a predetermined assist torque is generated in that motor.
That is, according to this assist control, the steering torque is detected from a twisting amount of a torsion bar or the like in which an input shaft coupled with a steering wheel and an output shaft coupled with a steering mechanism are connected to each other such that they can be rotated relatively to each other. A CPU computes a current instruction value based on this steering torque or the like and generates an assist force corresponding to the steering condition.
In the electrically-powered steering apparatus, not only the assist control based on the steering torque, vehicle velocity or the like but also a control taking into account the steering angle of a steering wheel, for example, self aligning control may be demanded depending on the case. In such a case, steering angle data detected by the steering angle sensor of the steering shaft needs to be inputted to the CPU.
However, the conventional electrically-powered steering apparatus needs to receive steering angle data detected by the steering angle sensor provided on the steering shaft through a control device provided separately from a control device for the electrically-powered steering apparatus. For this reason, data communication control needs to be provided between the both control devices and further, there arise various problems such as reliability of that data communication, securing of fail safe. Therefore, it has been considered that the assist control based on the steering angle is generally impossible.